no drive in reverse after it jumped out of gear

Was out tagging today in my defender and I have lost reverse.

Its an lt77 gearbox and it has been jumping out of reverse for a while now but today as I was holding it in gear it seemed to jump out of gear and then the gear stick went all floppy. I took the gator off and re located the stick and it was stuck in the reverse position but there was no drive. after about 5 mins of wiggling it finally went in to neutral. All 5 forward gears work fine with no noises. the reverse will go into position but no drive and no grinding noises.

Any ideas guys?

teeth on rev idler and layshaft wear ,quite a common fault on lt77, but its also possible selector lever is dislodged, its also important to check rev light switch doesnt impeded rev selection which it can if wound in too far

so if its not the rev light switch then its going to be a strip down?